Manufacture of mercuric oxide



Sept. 12, 1950 c. w. ROEN 2,521,949

MANUFACTURE OF MERCURIC oxm Filed March 9,-1948 3 Sheets-Sheet l INVENTOR CZ LL QL W. Fo n,

0- QWS ATTORNEY-5 Sept. 12, 1950 C. w. ROEN 2,521,949

MANUFACTURE OF MERCURIC OXIDE Filed March 9, 1948 3 SheeiSE-Sheet. 2

c INVENTOR Ma a ATTORNEYS Sept. 12, 1950 c. w. ROEN MANUFACTURE OF MERCURIC oxma.

" s Sheets-Sheet 5 Filed March 9, 1948 x. MM

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Patented Sept. 12, 1950 MANUFACTURE OF MERCURIC OXIDE Clarence W. Roen, El Cerrito, Califl, assignor to Precision Chemical Corporation, New York, N. Y., a corporation of California Application March 9, 1948, Serial No. 13,817

4 Claims. 1

This invention relates to the manufacture of mercuric oxide, better known commercially as red oxide of mercury, and has for its object the provision of certain improvements in its manufacture.

Mercuric oxide has heretofore been made by reacting elemental mercury with nitric acid to form nitrate of mercury, and converting the resulting nitrate to mercuric oxide by heat treatment. The process has been customarily carried out in two stages, as follows:

1st stage.-Acid and mercury were added in calculated quantities to an open pot, and allowed to react, with stirring. The reaction period was several hours, and the nitrate reaction product was in the form of a hard cake that had to be broken up and crushed for subsequent handling and treatment.

2nd stage.The crushed nitrate was then heated or calcined at a temperature of about 300-350 C. until the evolution of nitrogen oxides ceased and a hard cake of mercuric oxide was obtained. This cake had to be broken up by hand and crushed, and then ground to the desired fineness of the finished product.

Both stages were conducted in pots and no recovery of nitrogen oxide was attempted, and the loss of mercury was substantial. The time involved in carrying out the complete process was usually in excess of 24 hours.

The method of the invention is in effect a one stage operation in which there is substantially no loss of mercury, and which can be carried out in a very substantially shorter time than heretofore. In accordance with the invention, the nitric acid and mercury in stoichiometrical proportions to form mercurous nitrate are reacted in a rotating drum. The mercury is added to the nitric acid, in the drum, in small lots to avoid too violent initial reaction. As the mercurous nitrate forms it sticks and adheres to the interior cylindrical wall of the drum, and ultimately the wall is coated with a layer of the resulting mercurous nitrate reaction product. The drum is then heated, while continuing the rotation, and the mercurous nitrate is converted in situ to mercuric oxide. The entire process is carried out in the same rotating drum in a time interval of from 3 to 4 hours, without the necessity of any intermediate crushing or grinding of the mercurous nitrate. Moreover, the gases evolved in both the nitrating step and in the subsequent conversion step are recovered, resulting in the reclaiming of nitric acid and the recovery of volatilized mercury.

The foregoing and other novel features of the invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which Fig. 1 is a side elevation, partly in section, of a rotatable drum structure in which the method of the invention may be advantageously practiced,

Fig. 2 is a sectional elevation on the section line 2-'2 of Fig. 1,

Fig. 3 is an end elevation of the structure,

Fig. 4 is a side elevation of an apparatus, embodying the rotatable drum, for practicing the invention in its entirety.

A rotatable drum ID, of stainless steel or the like, is mounted within an insulated cylindrical body or housing H. The drum is rotatably supported by two exterior circular rails l2 and cooperating pairs of flanged rollers or trunnions I3. The two rollers l 3, on each side of the drum, are secured to a shaft I4 extending through the insulated end walls of the housing H and mounted in bearings l5. The bearings iii are mounted on a structural metal support frame It.

The charging and discharging end I"! of the drum is generally conical in shape, and has a circular opening adapted to be closed by a removable door l8. The door has a small central port normally closed by a readily removable plug l9. The other end of the drum has a circular plate 20 firmly secured to the drum and to a hollow shaft 2!. The shaft 2! passes through a guide bearing 22 in the end wall of the housing I l and a main bearing 23 suitably mounted on the frame iii. A sprocket 24 is socured to the outer end of the shaft 2!. An electric motor 25, mounted on a bracket 26 secured to the frame 16, is operatively connected through a chain drive 21 to a gear reduction 28. The last or low-speed pinion 29 of the gear reduction is connected by a chain 30 to the sprocket at, to drive the drum ID at about 3-4 R. P. M.

A pair of gas burners 3! are positioned below the rotary drum I0, and are appropriately supported in the insulation of the bottom of the housing ll. Each burner 3! is connected to the supply of fuel gas through a coupling 32 having a valve 33 for connecting and disconnecting its burner to the supply and for adjusting and controlling the amount of gas supplied to the burner. The insulated housing I! has a stack 34, having a damper 35, for the exhaust of the heating gases.

The end of the housing adjacent the conical end ll of the drum has a circular opening adapted to be closed by a door 36 having a hinge connection 31 with a bracket 38 secured to the frame IS. The door has a handle 36 and is adapted to be held closed by a sliding bolt 39 carried in apertured ears 40 of a bracket 4! secured to the frame l6.

Merely by way of example, a specific practice of the invention in the apparatus illustrated in the drawings will be described. With the doors l8 and 33 open, about 13 gallons of 42 Baumv (58% HNOs) nitric acid are introduced into the drum l0. From 20 to 30 pounds ofelemental mercury are then added to the The door I8 is then closed tight, and thedrum is rotated at 3 to 4 R. P. M. for 15 to minutes. If no vio; lent reaction occurs, which is indicated by the evolution of gas through the condenser (here-1 inafter described) rotation of the drum is stopped, and another 20 to 30 pounds of mercury is added. after this time interval, the heat ofreaction willhave raised the temperature of the drum contents to such a point'that it no longer will rise. Rotation oi the drum is again resumed. It is best at this stage to allow 15 to 20 minutes for rotation and observation. After the elapse of one-half to three-quarters of an hour since the first charge of mercury, the remainder of the mercury is added in one flask (7 6 pounds) lots, to a total of 4 flasks (304 pounds), this being the amount of mercury chemically required for reaction with the nitric acid to'form mercurous nitrate.

After all the mercury has been added, a time interval is preferably allowed for the ercury and acid tomix thoroughly without the application of heat. After approximately 15 minutes, the gas burners 3! are lighted with the fiainelow until the reaction has steadied itself After the period allowed for leveling oil or steadying, say about 1 hours from the introduction of the initial lot of mercury, the time switches and the merino-regulator are set and t e u ment needs o urther a en i n wi ea mp etion o l-the roc ss- W e abo /2 h ur a e s ed iro the sta tth a on it is des ra l t r o t i nqr in t e or r me i t ied a ist rm te h he e as b en hqre ehlr r n An con n ed evolut s it qges oxid wil be e denced by the aract r sti dd s -b own c. 9 of ni n d oxide N0 Whatever nitric oxide .(NQ) is evolved withinthe m s ediatel xid z d to emi spr es with h tmosph ref the cq r rsi n s not completed, ay b necessar oa lqw sm ths h ho r o so to mpl te th o ra ion.

he conve ted p oduct isal qved tqqqo clown in the drum for about one-half hour. The doors a d be o e ed slur-rue the qcolinedq n p iod- Th me cu i x de i r m vedf em h drum y s u shov an the ui men is ready o re a thw etmm n the firs st o h p rat on the i scury reacts with the nitric acid tov iorm mercur u i a w i h clings ro ist c att e nterior cylincl ifial wall of the drum. This wall of the d m i eie abl provide wit spl ra i y of sp e on itudinal li te bar 9 tin he mer u yan e 1 s th mix u o acid and mercury. Qrdinaril noexternalheating is usedduring the reactionof the mercury and nitric acid, the exothermic heat of reaction being suiiicient to heat the mixture to a temperau of o -.l50 0- H ve a h a i ea o l tio me i h heai nem be desirable to assure completion of the reaction within the contemplated tim interval of 1 to 2 hours. The heating at this stage should not raise the temperature of the charge in the drum above about C. It is only during the reaction of the mercury and acid that the process requires careful observation, to avoid too violent a reaction with possible loss of mercury. The completion of the reaction is determined by the elapsed time, and the gas burners are then turned on full and the time switches and thermo-regulator are set .tocontrol the subsequent conversion operation.

The .mercurous nitrate reaction product forms a coatingall around the cylindrical inner wall of the drum. The thickness of this coating depends upon the dimensions of the drum and the size of the charge, but may advantageously be about three-fourths of an inch. The coating remains n it as e edsesi he subse uent 99. qn omes news 1 ere uler a th a u i r en r c are e el eds ars rlt the m ur c xi i Obtained, in a reatise crystalline form, easily removed from the drum and readily ground to the customary iineness of commercial red oxide of mercury. liter example, the product removed fron fthe drum is at least 50% and usually ;60 to 90% through atoll p standard Tyler screen. This may-be ground to fall through a 325 mesh screen for marketing as pigment red oxide. The yellow oxide of mercury (and rm d e e p r des ma be. seduce by u t e e r ndin Qf the ed essen t e e ment i lumina e 'F 9 th r n for P ac in th icreni qn evolved d rin b th.mem ranesaed eve Stepsere w due di rqu he si de sin 'e her 43 to o e or liners re is dehsorptiqesewe 4- The gases 9 u tedr h drum l r u h a ine-4 s need W t -l e the lw l s n he i is .e ible qque pi v iiwi the top of h chamber .:3 P pe 1 at th gases ace M r h l w-ea th aim-h 43 to the tower 44 beneath thepackingv th ein.

' pr ys .48 de i r seidzfi othe ne itabsorbing medium) above the packing in the tower. Preferably, the liquid absorbing medium is recirculated throughthe tower by an'acid circulating pump 49. Ffrcsh water, dilute-acid, or other liquid absorbing mediummay be adde'd-to the recirculating liquid through a valved pipe 5B, and liquid maybe-withdrawnirom the sump in the tower bottom through a valved pipe 51. The condensate in the chamber 43 is withdrawn through a valved pipe 52. The gases exhausted from the tower 4 4 through a pipe 53 may be passed to another similar tower and so on until discharged tothe atmosphere or otherwise disposedof. By the use of severalabsorptlon towers in series, nitric acid oiapproximately 42-Be. m ay be reclaimed from the nitrogen oxides evolved during the process. Whatever mercury is vola-' tilized during the nitrating step as a result of tooviolent a reaction is condensedin the chamber 43 and recovered by withdrawal through the pipe 52.

During the conversion of the mercurous .nitrate to mercuric oxide the temperature of the drum contents should notexceed 3 50 CI, and is preferably between 3G0 and 350 .C. This temperature may be advantageously maintained by regulating the supply of gas to theburners 3| by means of a thermo-regulator 55 connected'to the valve 33. The thermo-regulator 55 is operatively connected to a thermo-couple oi othersuitable temperature responsive device St: in the exhaust pipe 34 of the drum. The temperature of the exhaust heating gas is sufficiently representative of the temperature of the drum contents, with a standardized procedure in a particular apparatus, for the contemplated thermo-regulation of the conversion step. The coupling 32, in the gas supply, has another control valve 51, in advance of the valve 33, which is operatively connected to a time switch mechanism 58. By setting this mechanism for a predetermined time interval, the valve 5'! will be closed and the supply of gas to the burner will be stopped after the elapse of that time interval. In practicing the invention, the mechanism 58 will be set to shut 01f the gas in a predetermined time interval (between 3 /2 to 4 /2 hours) after the first lot of mercury has been added to the nitric acid in the drum. Each of the burners 3| is provided with a time controlled valve 51-58, but the regulation of the temperature during conversion can usually be satisfactorily effected by providing only one of the burners with a thermo-controlled valve 33-55-54.

The advantages of the invention may be summarized as follows:

1. It is essentially a one-stage operation.

2. No loss of mercury by sublimation; consequently no danger of salivation to workmen and no loss of mercury.

3. 80 to 90% of the nitric acid is recovered for re-use.

4. The rotating drum avoids formation of the hard cake characteristic of the prior art practice. Porosity of the material during conversion results from even gas evolution, which in turn is the result of careful temperature control and timing.

5. A granular mercuric oxide product is directly obtained in the rotating drum.

6. Man hours required per unit poundage are approximately one-sixth that of the prior practice to produce a finished product ready for marketing.

7. Capital outlay for equipment to produce the same poundage in the same time is approximately one-fifth that of the prior practice.

I claim:

1. The method of making substantially granular mercuric oxide which comprises reacting a mixture of elemental mercur and nitric acid in a vessel rotatable about a substantially horizontal axis, rotating the vessel during the course of said reaction with the resulting production of mercurous nitrate in the form of a coating thereof on the interior surface of the vessel, and subsequently heating the rotating vessel to a temperature sufficiently high to effect decomposition of the mercurous nitrate while in situ in said coating with the resulting production of substantially granular mercuric oxide.

2. The method of making substantially granular mercuric oxide which comprises reacting a mixture of elemental mercury and nitric acid in a vessel rotatable about a substantially horizontal axis, rotating the vessel during the course of said reaction with the resulting production of mercurous nitrate in the form of a coating thereof on the interior surface of the vessel, effecting said reaction at a temperature not in excess of about C. by intermittently adding small lots of the mercury to the entire amount of nitric acid in the vessel, and subsequently heating the rotating vessel to a temperature sufhciently high to effect decomposition of the mercurous nitrate While in situ in said coating with the resulting production of substantially granular mercuric oxide.

3. The method of making substantially granular mercuric oxide which comprises reacting a mixture of elemental mercury and nitric acid in a vessel rotatable about a substantially horizontal axle, rotating the vessel during the course of said reaction with the resulting production of mercurous nitrate in the form of a coating thereof on the interior surface of the vessel, effecting said reaction in the rotating vessel over a period of 1 to 2 hours by intermittently adding small lots of the mercury to the entire amount of nitric acid in the vessel at such intervals as to prevent the development in the reaction mixture by the exothermic heat of reaction of a temperature in excess of about 150 C., and subsequently heating the rotating vessel to a temperature of BOO-350 C. for a period of 2 to 3 hours to effect decomposition of the mercurous nitrate while in situ in said coating with the resulting production of substantially granular mercuric oxide of such fineness that at least 50% passes through a 60 mesh standard Tyler screen.

4. The method of making substantially granular mercuric oxide which comprises reacting a mixture of elemental mercury and nitric acid in a vessel rotatable about a substantially horizontal axis, rotating the vessel during the course of said reaction with the resulting production of mercurous nitrate in the form of a coating thereof on the interior surface of the vessel, subsequently heating the rotating vessel to a temperature sufiiciently high to effect decomposition of the mercurous nitrate While in situ in said coating with the resulting production of substantially granular mercuric oxide, and subjecting the gaseous effluent from the reacting and heating operations to condensation for the recovery of mercury vapor and to absorption for the recovery of nitrogen oxide gases.

CLARENCE W. ROEN.

REFERENCES CITED UNITED STATES PATENTS Name Date Brusa Nov. 15, 1921 Number 

1. THE METHOD OF MAKING SUBSTANTIALLY GRANULAR MERCURIC OXIDE WHICH COMPRISES REACTING A MIXTURE OF ELEMENTAL MERCURY AND NITRIC ACID IN A VESSEL ROTATABLE ABOUT A SUBSTANTIALLY HORIZONTAL AXIS, ROTATING THE VESSEL DURING THE COURSE OF SAID REATION WITH THE RESULTING PRODUCTION OF MERCUROUS NITRATE IN THE FORM OF A COATING THEREOF ON THE INTERIOR SURFACE OF THE VESSEL, AND SUBSEQUENTLY HEATING THE ROTATING VESSEL TO A TEMPERATURE SUFFICIENTLY HIGH TO EFFECT DECOMPOSITION OF THE MERCUROUS NITRATE WHILE IN SITU IN SAID COATING WITH THE RESULTING PRODUCTION OF SUBSTANTIALLY GRANULAR MERCURIC OXIDE. 